Semiconductor integrated circuits (IC) typically include metallization layers used to connect various components of the IC, called interconnect, or back end of line (BEOL) elements. Copper often preferred over aluminum due to its lower resistivity and high electro-migration resistance. Copper interconnect, however, is typically difficult to manufacture with traditional photoresist masking and plasma etching used for aluminum interconnect.
One known technique for forming copper interconnects on an IC is known as additive patterning, sometimes called a damascene process, which refers to traditional metal inlaying techniques. A so-called damascene process may include patterning dielectric materials, such as silicon dioxide, or fluorosilicate glass (FSG), or organo-silicate glass (OSG) with open trenches where the copper or other metal conductors should be. A copper diffusion barrier layer (typically Ta, TaN, or a bi-layer of both) is deposited, followed by a deposited copper seed layer, followed by a bulk Copper fill, e.g., using an electro-chemical plating process. A chemical-mechanical planarization (CMP) process may then be used to remove any excessive copper and barrier, and may thus be referred to as a copper CMP process. The copper remaining in the trench functions as a conductor. A dielectric barrier layer, e.g., SiN or SiC, is then typically deposited over the wafer to prevent copper corrosion and improve device reliability.
With more features being packed into individual semiconductor chips, there is an increased need to pack passive components, such as resistors, into the circuits. Some resistors can be created through ion implantation and diffusion, such as poly resistors. However, such resistors typically have high variations in resistance value, and may also have resistance values that change drastically as a function of temperature. A new way to construct integrated resistors, called Thin-Film Resistors (TFRs) has been introduced in the industry to improve integrated resistor performance. Known TFRs are typically formed from SiCr (silicon-chromium), SiCCr (silicon-silicon carbide-chromium), TaN (tantalum nitride), NiCr (nickel-chromium), AlNiCr (aluminum-doped nickel-chromium), or TiNiCr (titanium-nickel-chromium), for example.
FIG. 1 shows a cross-sectional view of two example TFRs 10A and 10B devices implemented using conventional processes. Fabrication of conventional TFRs 10A and 10B devices typically requires three added mask layers. A first added mask layer is used to create the TFR heads 12A and 12B. A second added mask layer is used to create the TFRs 14A and 14B. A third added mask layer is used to create TFR vias 16A and 16B. As shown, TFRs 12A and 12B are formed across the top and bottom of TFR heads 12A and 12B, respectively, but in each case three added mask layers are typically required.
FIG. 2 shows a cross-sectional view of a known IC structure including an example TFR 30 formed in view of the teachings of U.S. Pat. No. 9,679,844, wherein TFR 30 can be created using a single added mask layer and damascene process. A TFR film 34, in this example a SiCCr film, may be deposited into trenches patterned into a previously processed semiconductor substrate. As shown, SiCCr film 34 is constructed as a resistor between conductive (e.g., copper) TFR heads 32, with an overlying dielectric region including a dielectric layer 36 (e.g., SiN or SiC) and a dielectric cap region 38 (e.g., SiO2) formed over the SiCCr film 34. The IC structure including TFR 30 may be further processed for a typical Cu (copper) interconnect process (BEOL), e.g., next level of via and trench. TFR 30 may be connected with other parts of the circuit using typical copper vias 40 connected to the copper TFR heads 32 for example.
Embodiments of TFR 30 may be particularly suitable for copper BEOL, which may have limitations regarding annealing (e.g., anneal temperature may be limited to about 200° C.). However, there is a need to construct TFR before metallization (either Cu or Al), so the TFR can be annealed at high temperature (e.g., around 500° C.) to achieve 0 ppm or near 0 ppm temperature coefficient of resistance (TCR). Also, there is a need or advantage (e.g., cost and time advantage) to reduce the number of mask layers required to construct the TFR. Further, there is a need for a TFR module formed using a damascene method for use in legacy technologies with aluminum interconnects, e.g., for high performance analog designs.